Merge pull request #3 from astonzhang/patch-1

Update materials.md

Author: tqchen

materials.md

@@ -15,4 +15,4 @@ More materials will be posted throughout the course.
 ## Materials on Deep Learning
 - [Deep Learning Book](http://www.deeplearningbook.org/) is a comprehensive material for the field.
 - [CS231n](http://cs231n.stanford.edu/) is a great course to get started on DL for vision.
-- [Deep Learning - The Straight Dope](http://gluon.mxnet.io/) contains useful tutorials and code.
+- [Dive into Deep Learning](http://en.diveintodeeplearning.org/) is an interactive open source book with code, math, and discussions.